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Based on how they bill it, it looks like it's running on VMs

Agreed. AWS RDS instance types are just EC2 instance types prefixed with "db." and you're choosing either single-AZ or multi-AZ deployments so presumably AWS is just spinning up 1 to 3 EC2 instances with some preconfigured software on them.

From what I know there is a secret sauce beyond a mere AMI and a control plane, based on some EBS volumes magic. I may be mixing things up with Aurora though.

this is very, very safe to assume. There is probably a hundred engineer's worth of "secret sauce" for an entire managed DB product line.

There were some comments in the early days that the Multi-AZ magic for classic RDS was just drbd on top of EBS.

Aurora is a completely different approach where the RDBMS code is modified to directly interface with EBS instead of going through a traditional OS filesystem layer.

Amazon published a paper describing how Aurora works:

https://www.allthingsdistributed.com/files/p1041-verbitski.p...

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